The present invention relates to methods for detecting the presence of organic vapors and more particularly to the use of antibody-coated test plates for detecting the presence of particular airborne organic material such as the vapors of narcotics.
The problems associated with the proliferation of narcotics need no great elaboration. "Narcotics" as used herein shall be defined broadly to include illicit drugs as defined by laws of the United States and by international convention. The term "narcotics" particularly includes opiates such as opium, morphine and heroin, as well as cannabinol and cocaine. The detection of narcotics is a concern of law enforcement officials. Since narcotics are often highly potent, quantities sufficient to provide numerous doses may be easily concealed.
The concealability of narcotics is especially problematic in law enforcement situations where the presence of drugs is a mere possibility. Customs officials may be constantly alert for narcotics, but the sheer impossibility of searching every package or every suitcase insures that quantities of narcotics will go undetected. If customs officials could know with a certainty when narcotics are in fact present, they could adjust their procedures accordingly.
Significant legal problems may prevent police officials from discovering narcotics even where they strongly suspect the presence of such drugs. Narcotics are often located where police need a warrant to search and, to obtain such a warrant, must be able to show probable cause. The ability to say with a certainty that narcotics are present might aid police in convincing a judge to issue a search warrant.
Animals, particularly dogs, have been employed to detect narcotic odors in the air. Dogs, however, cannot be taken everywhere. Furthermore, dogs are obvious, and an undercover law enforcement official cannot have a sniffing dog with him at all times. It would therefore be desirable to have a simple portable test device which will detect the presence of narcotics in a region before the narcotics are actually located.
Narcotics, as all chemicals, have particular vapor pressures. If vapors of a narcotic can be particularly identified within the atmosphere of a region, the presence of the narcotic may be assumed.
While chemical tests are available for substantially all narcotics to ascertain that a sample is or contains the particular narcotic, identifying their vapors is considerably more difficult. The vapor pressures of many solid substances, including most narcotics, is low and the concentration of molecules in the air will accordingly be low. Any test for vapors of a minimally volatile substance must be highly sensitive. Furthermore, such a test should be highly specific for the material to be identified, particularly when a single test is used to determine its presence. As opposed to a laboratory, where organic compounds to be identified may be isolated and subjected to a battery of tests for identification, a field test for vapors must particularly identify an unisolated compound, preferrably in a single test even at low levels and in the possible presence of vapors of other similar compounds.
The high degree of specificity needed to detect vapors of particular organic material is found in biological systems, e.g., the olfactory system of dogs. On a molecular level, certain proteinaceous compounds, such as antibodies found in the immuno-systems of organisms, may be extremely selective and may react with a single compound or at least a very limited class of related compounds.
While antibodies produced by the immuno-systems of organisms generally are specific for particular macromolecules such as foreign proteins, various immunological techniques have been developed to "trick" organisms into producing antibodies which will react with and are specific for many small or medium size organic molecules.
Antibodies, due to their high degree of specificity, have been used to test for the presence of trace amounts of particular organic material, e.g., Lukens and Williams, Environmental Science and Technology, 11, pp 292-297 (1977). If antibodies are to be used to detect trace amounts of organic vapors, it is necessary to expose the antibody molecules to the atmosphere in a manner which allows for binding of the particular organic material thereto and in a manner by which the complexing of the antibody and the organic vapor may be definitively observed.
U.S. Pat. No. 4,054,646, issued Oct. 18, 1979, to Giaever, describes a number of test plates for immunological tests by which solutions may be tested for the presence of various immunologically active compounds including antibodies, antigens and haptens (incomplete antigens). The test plates described in U.S. Pat. No. 4,054,646 are glass slides coated with a thin layer of metal which, in turn, is coated by an antibody or an antigen (a chemical to which an antibody specifically binds). When such test plates are submerged in a solution containing the corresponding antigen or antibody, an antigen-antibody complex is formed on the surface thereof which results in a change of the light transmittance or the light reflective characteristics of the test plate. Such test plates make efficient use of antibody or antigen (either of which may be very expensive to produce and/or isolate) by distributing the immunological material (antibody or antigen) over a large surface area to maximize its exposure. The shiny surface of the metal layer is particularly suitable for accentuating changes in the optical properties resulting from the formation of the complex.
The adaption of antibody-coated test plates to the detection of airborne vapors would permit simple quick testing for particular organic material to be done in the field. While antibody-coated test plates have been described, most test plates actually developed are antigen coated plates used to detect antibodies in solution. While antibody-coated plates have been described which test for antigens or haptens in solution, few such antibody-coated test plates have been developed due to problems particular to applying antibodies to test plates in a manner that the antibody remains reactive with the organic material to which it is specific.
Antibodies tend to coat a metal surface in a preferred orientation which may be antithetical to the binding of the antibody to the organic material to which it is specific. Antibodies generally have a large number of active groups aligned in a particular orientation so as to specifically bind with a particular organic material or with a limited class of organic materials. When exposed to a metal surface, these active groups may react with the metal to bind the antibody thereto in a particular alignment. If the active sites necessary to recognize the particular organic material are bound to the metal, the antibody is unable to complex with the organic material.
Immunoglobulin type G antibodies, the type of antibodies found most commonly in the blood of mammals and hence the most easily obtained, have an Fab end which generally contains the binding sites for the particular organic material and an Fc end which generally does not bind to the particular organic material. When type G antibody is applied to a metal surface, the tendancy is for the Fab rather than the Fc end to bind with the metals. Fab-metal binding obscures the sites available for complexing, and, thus, unless the natural tendency for Fab-metal binding is overcome, few binding sites will be available for binding with the organic material. While some Fc-metal binding will occur, the loss of available specific binding sites due to Fab-metal binding is especially problematic in developing test plates for vapor detection where the amount of the particular organic material available for binding is generally far less than is available in solution.
It is a primary object of the present invention to provide a method of detecting the presence of airborne organic material, particularly the presence of narcotic vapors, within a region. It is a further object of this invention to adapt antibody coated test plates to the detection of vapors of particular organic materials.